Simple shader to make a cubic map from 6 / 12 inputs. Each input is from a 960 x 960 or 1k x 1k (for the matte version) pixel image of the different camera views. The matte version is for compositing over existing 360 bg.

Each camera is set to 90 degree FOV and pointed in the 6 different directions to create a 360 degree image. After making the cubic you can use the map convert tool to make it into a cylindrical or spherical map for uploading to youtube.